1. Field of the Invention
The present invention relates to a novel release agent and a manufacturing method of a release paper with use thereof and more particularly, pertains to a novel release agent which is substantially free of migration into the layer of any pressure sensitive adhesive and a method of efficiently and economically manufacturing release paper with use thereof by way of extrusion lamination or coating process.
2. Description of the Prior Art
Heretofore, the manufacturing method of silicone base release paper is principally based on a coating process, in which usually, a layer of laminated polyethylene is formed on a substrate like paper, etc., and further, a release layer is coated on the surface thereof. The release agent employed in this process consists of polymethyl hydrogen siloxane and vinyl group containing polydimethyl siloxane, and addition of platinum catalyzer and heat induces their addition reaction, causing curing and formation of release coating. According to this process, however, it thus needs to be prepared by mixing the ingredients and subjecting the mixture to the addition reaction. This process involves not only problems in insufficient curing, short pot life, etc., but difficulties in practical uses because of complicated operation and handling.
On the other hand, the release layer may be formed on the substrate at once by extrusion lamination process. The resin laminated in this way itself has a certain releasability. As such releasable resins, ethylene-.alpha.-olefin copolymer elastomer, etc., are used and they are preferable for acrylic pressure sensitive adhesives. In the aforementioned extrusion lamination process, however, there is apprehension regarding heat and solvent resistance, etc., at the time of coating of acrylic pressure sensitive adhesives and scattering of release potential with regard to the acrylic pressure sensitive adhesives and the release strength becomes heavier with the lapse time. Since ethylene-.alpha.-olefin copolymer elastomer, when singly used, is difficult to extrude, it is used in mixture with polyethylene. The smaller the mixing proportion of said elastomer, the more releasing effect will be lost; but conversely, with its increasing proportions, said elastomer's property will become stronger, and the film strength lower; moreover, such problems in processing as blocking, etc., will be induced.
And in Patent Publication No. Sho 60-5628, a releasable laminate film formed by laminating on a substrate a thermoplastic resin prepared with addition of non-cure type organopolysiloxane is proposed. But such a releasable laminate film shows high resistance to release and produces bleeding to the surface of silicone even at room temperature; therefore, it can not necessarily be said adequate for pressure sensitive adhesive tapes or sheets.
The present inventors, in an effort to overcome such problems hereabove-mentioned, developed a manufacturing method of a release agent which comprises extruding a mixture of a silicone base release agent and polyolefin and, then, getting said release agent bled to the surface by subjecting it to a heat-treatment, followed by fixing by curing, as described in U.S. Pat. No. 4,702,874. Said method, however, is disadvantageous in that it requires a curing treatment by treatment with such a catalyzer as chloroplatinic acid, etc.